The human mineralocorticoid receptor (MR) serves as the final effector of the renin-angiotensin-aldosterone pathway and is a key regulator of sodium homeostasis in the distal nephron. These investigators recently described a novel form of human Mendelian hypertension caused by a gain of function mutation novel form of human Mendelian hypertension caused by grain of function mutation in MR. The mutation results in constitutive activity of the receptor and alters receptor specificity such that progesterone, normally an MR antagonist, functions as an agonist. Consistent with the dramatic rise in progesterone levels in pregnancy, carriers of this mutation develop severe pregnancy-related hypertension. Previous studies indicate that bending of helix 3, and that this mutant achieves the 21-0H independent bending of helix 3 via creation of a novel van der Waals interaction between helix 3 and helix 5. The observations that this helix 3- helix-5 interaction is highly conserved among diverse nuclear receptors indicated its general role in receptor activation. In this grant, we propose both biochemical and clinical studies to augment our understanding of MR function in human physiology and hypertension. They will assess the proposed model for MR activation and identify specific residues necessary for MR specificity and activity. Furthermore, they will identify nuclear co-regulators required for MR activity and identify the biochemical requirements for MR activation. Clinically, they propose to determine the prevalence of disease causing MR mutations in a variety of clinical situations and finally, determine extra-renal effects of an activated MR in patients carrying this mutation.